The present invention relates to vehicular headlamps, and more particularly to a novel vehicular headlamp having a discharge lamp as its light source and in which electromagnetic noise attributed to a high voltage section is minimized and the operating stability of the headlamp is improved.
Application of a discharge lamp such as a metal halide discharge lamp as the light source of a vehicular headlamp has been proposed. However, in order to turn on a discharge lamp, it is necessary to provide a lighting circuit for applying a high discharge voltage to the discharge lamp. In the case of a conventional vehicular headlamp of this type, the lighting circuit is supported on the vehicle body separately from the headlamp, and is connected through insulated lead wires to the headlamp.
However, in the case where the lighting circuit is supported on the vehicle body separately from the headlamp as described above, the lead wires carrying the high voltage are exposed where they can be reached by the hand of the user, which is hazardous. In addition, the lead wires, which are relatively long, radiate electromagnetic noise, thus adversely affecting electronic circuits and other components on the vehicle.
Further, recently in the motor vehicle lamp industry, development efforts have been directed to a discharge lamp which is excellent in light emission efficiency and in its output light spectrum characteristics and which has a long service life, and extensive research has been carried out on the use of a discharge bulb as the light source of a motor vehicular headlamp.
FIG. 1 shows a headlamp of such a type, which includes a lighting-circuit-accommodating unit 4 which encases a circuit used to start the discharge operation of a discharge bulb 2. The unit 4 is mounted on the rear side of a lamp body 1 in which a discharge bulb 2 is inserted. Reference numeral 6 designates a lens mounted on the front end of the lamp body 1.
In the above-described conventional headlamp, the lighting-circuit-accommodating unit 4 is secured to the lamp body 1 only with screws. Hence, in order to secure the lighting-circuit-accommodating unit 4 to the lamp body 1, it is necessary to turn the screws 5 with one hand while the unit 4 is being pushed against the lamp body with the other hand. This is a troublesome operation. Furthermore, the unit 4 may come loose from the lamp body 1 when vibrated because it is fastened to the lamp body only with the screws.